linux-kernel - Re: [PATCH v7 06/16] firmware: arm_scmi: Add configurable polling mode for transports

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Message-ID: <20211213112555.vhjhu3xopesvxmio@bogus>
Date:   Mon, 13 Dec 2021 11:25:55 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Cristian Marussi <cristian.marussi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        james.quinlan@...adcom.com, Jonathan.Cameron@...wei.com,
        f.fainelli@...il.com, etienne.carriere@...aro.org,
        vincent.guittot@...aro.org, souvik.chakravarty@....com
Subject: Re: [PATCH v7 06/16] firmware: arm_scmi: Add configurable polling
 mode for transports

On Mon, Nov 29, 2021 at 07:11:46PM +0000, Cristian Marussi wrote:
> SCMI communications along TX channels can optionally be provided of a
> completion interrupt; when such interrupt is not available, command
> transactions should rely on polling, where the SCMI core takes care to
> repeatedly evaluate the transport-specific .poll_done() function, if
> available, to determine if and when a request was fully completed or
> timed out.
> 
> Such mechanism is already present and working on a single transfer base:
> SCMI protocols can indeed enable hdr.poll_completion on specific commands
> ahead of each transfer and cause that transaction to be handled with
> polling.
> 
> Introduce a couple of flags to be able to enforce such polling behaviour
> globally at will:
> 
>  - scmi_desc.force_polling: to statically switch the whole transport to
>    polling mode.
> 
>  - scmi_chan_info.no_completion_irq: to switch a single channel dynamically
>    to polling mode if, at runtime, is determined that no completion
>    interrupt was available for such channel.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> ---
> v5 --> v6
> - removed check on replies received by IRQs when xfer was requested
>   as poll_completion (not all transport can suppress IRQs on an xfer basis)
> v4 --> v5
> - make force_polling const
> - introduce polling_enabled flag to simplify checks on do_xfer
> v3 --> v4:
> - renamed .needs_polling flag to .no_completion_irq
> - refactored error path when polling needed but not supported
> ---
>  drivers/firmware/arm_scmi/common.h | 11 +++++++++++
>  drivers/firmware/arm_scmi/driver.c | 17 +++++++++++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
> index 6438b5248c24..99b74f4d39b6 100644
> --- a/drivers/firmware/arm_scmi/common.h
> +++ b/drivers/firmware/arm_scmi/common.h
> @@ -339,11 +339,19 @@ void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id);
>   * @dev: Reference to device in the SCMI hierarchy corresponding to this
>   *	 channel
>   * @handle: Pointer to SCMI entity handle
> + * @no_completion_irq: Flag to indicate that this channel has no completion
> + *		       interrupt mechanism for synchronous commands.
> + *		       This can be dynamically set by transports at run-time
> + *		       inside their provided .chan_setup().
> + * @polling_enabled: Flag used to annotate if polling mode is currently enabled
> + *		     on this channel.
>   * @transport_info: Transport layer related information
>   */
>  struct scmi_chan_info {
>  	struct device *dev;
>  	struct scmi_handle *handle;
> +	bool no_completion_irq;
> +	bool polling_enabled;

Do we really need a separate flag for polling_enabled ?
no_completion_irq means you need to enable polling and force_polling too.
Just trying to see if we can get rid of unnecessary flags.

-- 
Regards,
Sudeep